Ion sources generate a large amount of heat during operation. The heat is a product of the ionization of a working gas, which results in a high-temperature plasma in the ion source. To ionize the working gas, a magnetic circuit is configured to produce a magnetic field in an ionization region of the ion source. The magnetic field interacts with a strong electric field in the ionization region, where the working gas is present. The electrical field is established between a cathode, which emits electrons, and a positively charged anode, and the magnet circuit is established using a magnet and a pole piece made of magnetically permeable material. The sides and base of the ion source are other components of the magnetic circuit. In operation, the ions of the plasma are created in the ionization region and are then accelerated away from the ionization region by the induced electric field.
The magnet, however, is a thermally sensitive component, particularly in the operating temperature ranges of a typical ion source. For example, in typical end-Hall ion sources cooled solely by thermal radiation, discharge power is typically limited to about 1000 Watts, and ion current is typically limited to about 1.0 Amps to prevent thermal damage particularly to the magnet. To manage higher discharge powers, and therefore higher ion currents, direct anode cooling systems have been developed to reduce the amount of heat reaching the magnet and other components of an ion source. For example, by pumping coolant through a hollow anode to absorb the excessive heat of the ionization process, discharge powers as high as 3000 Watts and ion currents as high as 3.0 Amps may be achieved. Alternative methods of actively cooling the anode have been hampered by the traditional difficulties of transferring heat between distinct components in a vacuum.
There are also components in an ion source that require periodic maintenance. In particular, a gas distribution plate through which the working gas flows into the ionization region erodes during operation or otherwise degenerates over time. Likewise, the anode must be cleaned when it becomes coated with insulating process material, and insulators must be cleaned when they become coated with conducting material. As such, certain ion source components are periodically replaced or serviced to maintain acceptable operation of the ion source.
Unfortunately, existing approaches for cooling the ion source require coolant lines running to and pumping coolant through a hollow anode. Such configurations present obstacles for constructing and maintaining ion sources, including the need for electrical isolation of the coolant lines, the risk of an electrical short through the coolant from the anode to ground, degradation and required maintenance of the coolant line electrical insulators, and the significant inconvenience of having to disassemble the coolant lines to gain access to serviceable components, like the gas distribution plate, the anode, and various insulators.